Pressure cycle for stimulating blood circulation in the limbs

ABSTRACT

A method of cycling pressure applied externally to a mammalian limb to obtain high amplitude surges of blood. A fast rise time followed by a holding period and a relatively long relaxation interval is utilized.

United States Patent 1191 Nicholson et al.

1451 Aug. 26, 1975 PRESSURE CYCLE FOR STIMULATING [56] References CitedBLOOD CIRCULATION IN THE LlMBS UNITED STATES PATENTS Inventors: James E.Nicholson, Quincy; Charles 2,145,932 2/1939 Israel 128/299 S. Lipson,Newton, both of Mass. 2,225,308 12/1940 Kroll 128/299 3,063,444 11/1962.lobst 128/24 R Ass1gnee: Clinical Technology International,

Canton Mass Primary Examiner-Lawrence W. Trapp Filed: Apr. 8, 1974Attorney, Agent, or Firm-Thomas N. Tarrant pl 0 45 [57] ABSTRACT? Amethod of cycling pressure applied externally to a :LtSkgl 2 mammalianlimb to obtain high amplitude surges of n blood A fast rise timefollowed by a holding period Field of Search 128/24 53 and a relativelylong relaxation interval is utilized.

' 6 Claims, 4 Drawing Figures '5 I 60 I I E 50- E 40F Lu 3O t O a 20 U)10 LU i4" O 10 llllillllllllllllllillllilllljllllillllilllll 0 IO 20 3O4O 5O 6O 7O 80 TIME (Sec) PRESSURE (mm Hg) BLOOD FLOW (ML/MIN)PATENTEBAUGZBIQYS 3,901,221

SHEET 1 BF 2 Ill! TIME (Sec) PATENTED AUG 2 6 I975 SIIZU 2 0? 2 TIME(Sec.)

FIG. 4

PRESSURE CYCLE FOR STIMULATING BLOOD CIRCULATION IN THE LIMBS BACKGROUNDOF THE INVENTION 1. Field of the Invention The invention relatesto'pressure garments used to apply cyclical pressure to mammalianextremities for the purpose of overcoming circulatory defficiency andparticularly to a pressure cycling method.

2. Relation to the Prior Art Roberts et al (The Effect of IntermittentlyApplied External Pressure on the Haemodynamics of the Lower Limb in Man,British Journal of Surgery, 1972, Vol. 59 No. 3 March) disclosed thatwhen pressure was appliedto the legs with an inflatable plastic splint,increase in peak venous flow was directly proportional to the rate ofpressure application. He purported to demonstrate that the peak increasein blood flow was maximal atan inflation rate of mm. Hg. per second andthe maximums in pulsatility and peak flow required an approximateinterval of one minute between applications of pressure.

The primary interest in such dynamic stimulation of blood today is tocombat the high rate of postoperative deep-vein thrombosis. Theformation of dangerous thrombi is promoted by pockets of blood stasis.Blood stasis in the limbs is normally prevented by physical activity.Since surgery both prevents normal activity and exposes the system to,coagulant stimulating effects, a high. rate of thrombosis results.Increasing peak flow and pulsatility tends to overcome pockets ofstasis.

While Roberts et al. disclose conditions of peak increased flow andmaximum increase in pulsatility with respect to repetition intervals,they neglect the amplitude of flow during each pressure applicationconcerning themselves only with peak increase.

SUMMARY OF THE INVENTION In accordance with the present invention, ithas been found that blood stasis pockets in the veins of mammalianextremities occur particularly behind the cusps which form thedirectional valves of the veins. It has been found that optimumdisturbance of stasis behind these cusps is obtained when pulses ofincreased flow level have a maximum amplitude; that is, when as large aquantity of blood as is comfortable passes these cusps during a givenpulse. It has been found that this result can be obtained by applyingpressure through a pressure garment with a rise time of at least 10 mmof mercury per second and a holding time at the level of at least 30 mmof mercury for at least 8 seconds. A cycle period of one minute is nearoptimum.

Thus, it is an object of the present invention to provide a novelpressure cycling method for cycling pressure garments so as to overcomeblood stasis in mammalian extremities.

It is a further object of the present invention to provide a method ofpressure cycling for application to the external mammalian limb tomaximize the amplitude of increased flow pulses by a pressure holdingtime of at least 8 seconds.

Further objects and features of the invention will become apparent uponreading the following description together with the drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a graph of a controllerpressure cycle ac cording to the invention.

FIG. 2 is a graph of femoral vein flow resulting from the pressure cycleof FIG. 1.

FIG. 3 is a diagrammatical illustration depicting operation of theinvention.

FIG. 4 is a graph of exemplary internal boot pressure resulting from thecontroller cycle of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT:

FIG. I is a graph of pressure at the cyclic controller output inaccordance with the preferred pressure cycle. When the pressure line isconnected to the boot by operation of a valve at time zero, curveportion 10 indicates a rapid rise in less than 4 seconds to greater than30 mm of mercury. The pressure then climbs gradually above 40 mm ofmercury as indicated by curve 1 1 until l0 seconds is reached at whichpoint the pressurizing valve is closed and the exhaust valve opening tothe atmosphere is opened so that at 12 seconds the pressure has droppedbelow 10 mm as depicted by curve 12. For the following 48 secondtimeperiod, depicted by curve 14, no pressure is applied allowing theblood veins to refill. The cycle repeats at 60 second intervals.

FIG. 2 depicts flow in the superficial femoral vein during the pressurecycle of FIG. 1. Pulses 15 are normal blood pulsation provided by theheart. The normal flow level, in the particular instance depicted,averaged slightly over 50 milliliters per minute. Upon application ofpressure from the pressure boot, the flow increased over an interval ofapproximately 2 seconds to approximately milliliters per minute, asindicated by curve 16. Curve l7 depicts the slow dropping off virtuallyimmediately after reaching its peak. The pressure is releasedapproximately at point 18 in the curve whereupon the flow drops tobaseline level and flows for a short interval at a rate less thanbaseline level as indicated by inverted peak 20. The blood flowcharacteristics remain below average normal blood flow for the following28 seconds as indicated by portion 21 of the graph. The blood thenreturns to the normal flow characteristics prior to the next pressurepulse depicted by curve 22.

The operation of the present invention is best understood by descriptionof its utilization with a human being. Referring to FIG. 3, a patient25, depicted as lying down, wears a boot 26 enclosing his foot and lowerleg to the vicinity of the knee and also a mitten 27 enclosing his handand forearm. Both boot and mitten are made of outer and inner layer withan inflatable space therebetween. The outer layer in each case haslimited expandability so that, upon inflation, pressure is directedinward against the enclosed limb. Boot 26 and mitten 27 are inflatedthrough hoses 28 from a pressure tank 30. Pressure tank 30 may beconnected to a pump for continuous duty use. Between pressure tank 30and hoses 28 is a cyclic controller 34 for applying and releasingpressure in accordance with the graph in FIG.

FIG. 3 depicts operation of one boot and one mitten. The pressurecycling of the invention can be applied to any one or more of the fourlimbs.

FIG. 4 shows pressure measured inside a boot during a controllerpressure cycle according to FIG. I. The

rise time inside the boot is 40 mm Hg. in approximately 4 seconds asshown in curve 35. The fall time shown by curve 36 is likewise a littleslower falling to lO mm Hg. in about 2 seconds and then curvingexponentially to over the next 8 seconds.

' While the invention has been described in accordance with a preferredembodiment, some latitude in the operation of the cycle is desirabledepending on specific patients and conditions. A rapid boot pressurerise to at least 30 mm of mercury produces near optimum results whenextended over 3 seconds. With particularly sensitive patients, this risemay be extended out to seconds to reduce discomfort. Similarly, themaximum pressure attained is desirably between 40 and 50 mm of mercury,but a peak of 30 mm of mercury is sufficient for most cases. A range of9 to seconds is acceptable for the time interval between the beginningof pressure application and the onset of pressure release. For maximumeffect it is desirable to delay the next application of pressure untilthe venous flow has returned to its normal equilibrium point, however,this differs with the individual patient and may vary within a fairlywide range with a total period between the cyclical commencement ofpressure application being anywhere from about 40 to 80 seconds. Aperiod of 60 seconds is suitable for most cases.

Using the pressure cycle depicted in FIG. 1, it has been found that inan average case the total increase in blood flow over the 12 secondinterval beginning with the first application of pressure isapproximately 30% more than if the pressure is released immediatelyafter the peak pressure is attained. Thus the holding period afterattaining the peak pressure has a significant effeet.

Having described a preferred example of the invention along with anindication of the ranges of variation within its scope, the followingclaims set forth the scope to be covered.

We claim:

1. A method of overcoming circulatory stasis in mammalian limbscomprising:

a. Applying to a limb portion fluid pressure of at least 30 mm ofmercury over a time interval of between 9 and 15 seconds with a risetime reaching 30 mm of mercury within 3 seconds;

b. keeping the applied pressure below 1 mm of mercury over a timeinterval of 30 to 60 seconds; and

c. cyclically repeating the above steps.

2. A method according to claim 1 wherein said pressure is applied forsubstantially 12 seconds and removed for substantially 48 seconds inrepeating cyclical fashion.

3. A method according to claim 1 wherein said fluid pressure is in therange of 40 to 50 mm of mercury and has an inflation rate reaching atleast 10 mm of mercury per second for at least 3 seconds.

4. A method according to claim 3 wherein said fluid is a gas.

5. A method according to claim 4 in which said fluid is applied by meansof a plastic garment enclosing a limb extremity.

6. A method according to claim 4 wherein at the end of the said timeinterval over which the fluid pressure in the range of 40 to 50 mm ofmercury is applied, the pressure is released falling to 10 mm of mercuryin about 2 seconds and then more slowly to 0 mm of mercury.

1. A method of overcoming circulatory stasis in mammalian limbscomprising: a. Applying to a limb portion fluid pressure of at least 30mm of mercury over a time interval of between 9 and 15 seconds with arise time reaching 30 mm of mercury within 3 seconds; b. keeping theapplied pressure below 1 mm of mercury over a time interval of 30 to 60seconds; and c. cyclically repeating the above steps.
 2. A methodaccording to claim 1 wherein said pressure is applied for substantially12 seconds and removed for substantially 48 seconds in repeatingcyclical fashion.
 3. A method according to claim 1 wherein said fluidpressure is in the range of 40 to 50 mm of mercury and has an inflationrate reaching at least 10 mm of mercury per second for at least 3seconds.
 4. A method according to claim 3 wherein said fluid is a gas.5. A method according to claim 4 in which said fluid is applied by meansof a plastic garment enclosing a limb extremity.
 6. A method accordingto claim 4 wherein at the end of the said time interval over which thefluid pressure in the range of 40 to 50 mm of mercury is applied, thepressure is released falling to 10 mm of mercury in about 2 seconds andthen more slowly to 0 mm of mercury.